Bimetallic PdII complexes with NHC/Py/PCy3 donor set ligands: applications in α-arylation, Suzuki-Miyaura and Sonogashira coupling reactions

Bimetallic complexes bearing NHC donor ligands are gaining immense popularity as catalysts in organometallic chemistry. However, such complexes with a mixed NHC/PR3 donor set ligands are still rare. We present here a series of bimetallic Pd-II complexes featuring mixed NHC/Py/PCy3 donor set ligands applied in alpha-arylation of amide, Suzuki-Miyaura coupling and Sonogashira coupling reactions. All complexes have been characterized using standard characterization techniques and one of the complexes has been structurally characterized by X-ray crystallographic analysis. Catalytic outcomes clearly indicate the superior activity of Pd-II complex bearing mixed NHC/PCy3 donor set ligands compared to the PEPPSI-type complexes in both alpha-arylation of amide and Sonogashira coupling reactions, though almost similar activities were observed for all the complexes in Suzuki-Miyaura coupling reactions. This observation might be due to the involvement of Pd-NPs as an active catalyst in Suzuki-Miyaura coupling reactions, whereas the Hg-poison test suggested the homogeneous nature of the other two types of reactions. Two pyridine rings in a mixed NHC/4-OMe(Py) donor complex are oriented almost in a parallel face-to-face fashion with a centroid to centroid separation of 3.758 angstrom, indicating pi center dot center dot center dot pi interactions between two methoxypyridine rings. This interaction leads to a very short Pd center dot center dot center dot Pd distance of 5.754 angstrom in the aforementioned complex.

Automated summary

Bimetallic Pd-II complexes with mixed NHC/Py/PCy3 donor set ligands have been synthesized and evaluated as catalysts in various reactions. The complexes showed superior activity in the alpha-arylation of amide and Sonogashira coupling reactions compared to PEPPSI-type complexes.